The invention relates to an apparatus for forming, in particular injection molding, products comprising at least one natural mono- or polymer.
In the international patent application WO 96/30186, a method is described for injection molding products from a mass comprising at least natural polymers such as starch. To that end, the mass is introduced into a closed mold cavity and is pressurized therein, while the mold cavity is heated to a temperature at which, initially, gelatinization of the natural polymers and, then, cross linking thereof occurs. In the mass, a blowing agent, for instance water, is included, which is brought to the boil in the mold cavity and consequently blows bubbles into the mass such that cells are formed therein. In this method, the mold cavity is deaerated through one or more deaeration openings which are in communication with the surroundings, while an amount of mass is introduced into the mold cavity which is somewhat greater than required for completely filling the mold cavity. Thus, it is ensured that the mold cavity is optimally filled, while the surplus, the overdose, is discharged through the deaeration openings.
This method has the advantage that with it, in a particularly simple manner, products with a foamed wall structure can be manufactured from mass including natural polymers. In a comparable manner, for that matter, also natural monomers can be used.
A disadvantage of the apparatus used in this known method is that the blowing agent is discharged directly from the mold cavity, so that uncontrolled foam formation occurs in the mold cavity. Moreover, the overdose flows away through the deaeration openings to the surroundings, at least, to relatively cool surroundings, so that the desired gelatinization and/or cross-linking will not occur therein. This means that a ready product will bear relatively flexible, sticky parts, formed by the overdose, or that these parts will end up in the surroundings so that pollution or clogging of supply and/or discharge means occurs, that ready products will be polluted and like drawbacks. Moreover, such parts cannot be removed in a simple manner.